Layers of photographic elements other than the image-forming layer are commonly referred to auxiliary layers. There are many different types of auxiliary layers such as, for example, subbing layers, backing layers, interlayers, overcoat layers, receiving layers, stripping layers, antistatic layers and the like. Photographic elements often employ auxiliary layers comprising glassy, hydrophobic polymers such as polyacrylates, polymethacrylates, polystyrenes, or cellulose esters, for example. One typical application for such an auxiliary layer is as a backing layer to provide resistance to abrasion, scratching, blocking, and ferrotyping. Such backing layers may be applied directly onto the support material, applied onto a priming or "subbing" layer, or applied as an overcoat for an underlying layer such as an antistatic layer or the like. For example, U.S. Pat. No. 4,203,769 describes a vanadium pentoxide-containing antistatic layer that is overcoated with a cellulosic layer applied from an organic solvent. U.S. Pat. Nos. 4,612,279 and 4,735,976 describe organic solvent-applied layers comprising a blend of cellulose nitrate and a copolymer containing acrylic acid or methacrylic acid that serve as overcoats for antistatic layers.
When the auxiliary layer serves as the outermost layer, as is the case for a backing layer, it is desirable for this layer to have a low coefficient of friction (COF) to provide proper conveyance properties and to protect the photographic element from mechanical damage during the manufacturing process or customer use. It is known to protect photographic elements against mechanical damage by coating them with a layer comprising a lubricant such as a silicone fluid as described in U.S. Pat. No. 3,489,567, and a wax esters of high fatty acids or high fatty alcohols in U.S. Pat. No. 3,121,060. However, problems are encountered in the use of these lubricants. For example, when silicone is used as a lubricant for a backing layer, it may move to the surface of the support where a photographic element is to be coated. This will give an adverse effect (e.g. wetting) on the subsequent coating processes. They may also not survive processing so that the advantage of low surface friction is lost for the post-processed products. In addition, it has proven difficult to provide a single layer applied from organic medium that comprises both an abrasion-resistant polymer and a lubricant since it is difficult to find a coating medium that dissolves both the polymer and the lubricant and is at the same time attractive from an environmental and health standpoint. It is also difficult to form a stable dispersion of a lubricant such as a wax in an organic medium that may be added to a coating composition containing a dissolved, abrasion-resistant polymer. Therefore, in order to form a layer which can be applied from liquid organic medium that is both abrasion-resistant and has a low coefficient of friction one often applies two separate layers; a first layer which is comprised of an abrasion-resistant polymer and then a second layer which is comprised of a lubricant such as a wax. The need to apply these two separate layers increases both manufacturing complexity and cost.
Recent patent literatures have disclosed technologies for a photographic element to have a transparent magnetic recording layer for information and data recording and reading purposes. For example, U.S. Pat. No. 5,254,449 discloses the preparation and use of a substantially transparent magnetic recording layer in a novel photographic element. U.S. Pat. Nos. 5,427,900 and 5,432,050 describe transparent magnetic recording layers for use in photographic elements wherein organic solvents are used for the preparation of a dispersion containing the magnetic particles. U.S. Pat. No. 5,457,012 describes a magnetic recording layer formed from a dispersion of magnetic particles in an aqueous medium. The photographic element and particularly the transparent magnetic recording layer provided thereon must be capable of repeated use in both the recording and reading mode and, therefore, must be durable, abrasion resistant and scratch resistant so as not to adversely affect the quality of the photographic element. For example, during the residence of the film in a camera, entries may be made to the magnetic recording layer for every exposure, and an indeterminate number of read operations are conducted depending on the particular application to which the film is used. This also is true in the processing of the film and in subsequent use of the processed film for additional copies, enlargements and the like.
When a transparent magnetic recording layer is used as the outermost backing layer, excellent lubrication at its surface is required to lower the contact friction with the magnetic head and to allow for multiple transports of the film through various magnetic head-containing equipment. A lubricant could be added directly to the transparent magnetic layer. However, this typically weakens the layer and may result in premature rupture of the layer and loss of signal or recorded information. Furthermore, when the lubricant is added directly into the magnetic layer and coated and dried, the lubricant will be distributed throughout the magnetic layer and may not reside primarily at the surface where it is required for optimal performance. Alternatively, a separate lubricating layer is applied on the transparent magnetic recording layer. This of course reduces the manufacturing efficiency of the product by requiring several coating stations.
When a photographic element having a transparent magnetic recording layer as the backing layer is subjected to ordinary processing steps that differ from those related to ordinary magnetic tapes (e.g. audiotapes, and videotapes), new problem arises that staining materials, composed of ingredients in a developing solution, adhere to the back surface of the photographic element, and the said staining materials are transferred to the surface of a magnetic head at the time of the magnetic recording or reproduction after processing, which results in an error of magnetic input/output (an error in magnetic recording/reproducing). In order to solve such a problem, it is also effective to incorporate, into a backing layer, abrasives that are well known in the field of magnetic tape, for a silver halide photographic light-sensitive material having a transparent magnetic recording layer.
U.S. Pat. No. 5,798,136 describes a method of producing an imaging support which includes providing a support, simultaneously coating on a side of the support; a transparent magnetic recording layer comprising magnetic particles, a polymeric binder and an organic solvent, and a lubricating overcoat layer farthest from the support, the lubricating overcoat layer comprising wax particles having a size from 0.01 to 0.5 micron, and an organic solvent; and drying the magnetic recording layer and the lubricating overcoat layer. If the wax is dissolved in a solvent and coated simultaneously with the oxide layer, it can diffuse into the magnetic layer before the coating is dry. Thus, the amount of lubricant remaining at the surface is inadequate for proper lubrication. Since the diffusion rate is inversely proportional to the size of the dissolved lubricant, the wax dispersions, which are particles of sizes that are much larger than the radius of a dissolved long chain fatty acid or polymer, tend to remain at the surface during the coating process and provide adequate lubrication in the dried layer.
Aqueous wax dispersions of colloidal sizes (0.01 to 5 micron, typically in the range of from 0.01 to 1 micron) are generally known. Non-aqueous wax dispersions of colloidal sizes are difficult to prepare. Wax can be compounded into viscous non-aqueous media (viscosity greater than, for example, 1000 cps) by mechanical force. The problem with such an approach is that the particle size is difficult to predict and more difficult to reproduce. The resultant dispersions are not truly colloidal dispersions and on dilution wax particles will settle down or precipitate out. U.S. Pat. No. 5,798,136 has disclosed the preparation in acetone/methanol mixed solvents of polyethylene wax dispersions by first diluting the aqueous dispersions after dialysis. It has also disclosed the preparation of Carnauba wax dispersion in isobutyl alcohol by further ground using a ball mill of wax particle having an original size of greater than 2 microns.
U.S. Pat. No. 4,766,059 describes a method of making solid spherical beads having a mean size ranging form 0.5 to about 20 .mu.m. The polymer beads contain a polymeric resinous material and a water insoluble wax. The process of making such solid beads involves the use of water miscible or immiscible low boiling solvent to dissolve both polymeric materials and wax, and subsequently removal of the solvent or solvent mixture by evaporation. This requires large processing equipment and lengthy processing time, which increases the expenses. U.S. Pat. No. 5,695,919 describes a lubricant impregnated core/shell polymer particle, the polymer particle comprising a core portion which is insoluble in the organic medium and a shell portion which has an affinity for both the core portion and the organic medium.
JP 7181613A describes a top layer on the side of the transparent magnetic recording layer that contains wax with an average grain size between 0.01 and 3 microns. However, the content of the wax in the layer is less than 50 weight percent of the binder. JP 7181612A claims an oxidized polyethylene wax (with an acid value of 5-55 and unsaturated terminals) on the transparent magnetic layer.
This invention provides the photographic element having a transparent magnetic layer with an improved lubricant layer that demonstrates excellent manufacturability, improved magnetic performance, improved running durability and scratch resistance, and improved resistance to stain materials during photographic processing.